The present invention relates to a toothbrush which can effectively remove dental plaque or foreign matters deposited on teeth without hurting gingiva or gums.
Recently, it has been elucidated that both the two most significant dental diseases, dental caries and periodontosis, are caused by dental plaque. Accordingly, in order to protect teeth against such diseases, it has been found that it is preferable to carry out a brushing method, such as a scrubbing method, a Fones' method, or a Bass method, by which dental plaque can be effectively removed by utilizing the tip ends of bristle tufts of a toothbrush. Since the tip ends of bristle tufts are made into contact with the gums while giving a considerably strong pressing force against the gums in such a brushing method as described above, relatively soft or fine bristles are implanted in a block head (tuft-implant portion) of a conventional toothbrush developed for the purpose of use for carrying out the above-mentioned brushing method so as to prevent the gums from being hurt.
Recently, as a result of studies in which a pressure sensor was disposed on a teeth surface so as to investigate the correlation among the diameter of bristles of a toothbrush, the brushing pressure, and the dental plaque removing effect, it was found that the thicker the bristles, the stronger the brushing pressure and the more superior the dental plaque removing effect as described, e.g., in J. Japan. Ass. Periodont., Vol. 28, pages 1,120 to 1,130 (1986). Accordingly, it has been found that it is preferred to make the diameter of the bristles to increase the brushing pressure in view of the purpose of the dental plaque removing. On the other hand, however, there is also a fact that the use of fine bristles are preferable in order to prevent gums from being hurt. These two facts have a relationship of antinomy to each other.
As a means for solving such an antinomy, it can be considered to provide a method in which the brushing pressure is made high by making the bristle tuft-implantation density high while using fine bristles. However, in order to realize this method, it is necessary to make tuft holes formed in a block head large in diameter, or to make the density of the tuft holes high. There is a problem that the touch of bristle tufts becomes hard so as to make the feeling of use poor when the tuft holes are enlarged in diameter, while there is another problem that the block head is apt to be broken due to mechanical fatigue or a chemical action when the density of the tuft holes is made high. In either case, there is still another problem that water is hardly drained to cause an insanitary state after use of a toothbrush because the intervals between the tuft holes are narrow. In order to solve the foregoing problems, the present inventor has thought of an idea to make bristle tufts slant.
Conventionally, the slanting arrangement of bristle tufts per se is known as disclosed e.g., in Japanese Utility Model Publication No. 31095/79 and Japanese Utility Model Application (OPI) Nos. 121765/74 and 3972/72 (the term "OPI" used herein means a "published unexamined Japanese Patent or Utility Model Application"), U.S. Pat. Nos. 3,722,020, 4,010,509, 4,051,571, 4,081,876, 4,115,894, 4,137,593, 4,291,431, 4,382,309, and 4,493,125. In these prior arts, the slanting arrangement is employed, e.g., in order to brash effectively the difficult tooth area such as the lingual of the lower teeth, etc.; in order to clean the gap of the teeth; in order to aid brushing by the rolling method; or the like. These prior arts, however, have not been directed to make the brushing pressure high, and therefore the arrangement is not suitable for making the brushing pressure high. As the result of investigation on the position as well as the slanting direction of the bristle tufts to be slanted on the block head of a toothbrush, the present inventor has achieved the present invention.